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__init__.py
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"""
This module contains backports the data types that were significantly changed
in the transition from Python 2 to Python 3.
- an implementation of Python 3's bytes object (pure Python subclass of
Python 2's builtin 8-bit str type)
- an implementation of Python 3's str object (pure Python subclass of
Python 2's builtin unicode type)
- a backport of the range iterator from Py3 with slicing support
It is used as follows::
from __future__ import division, absolute_import, print_function
from builtins import bytes, dict, int, range, str
to bring in the new semantics for these functions from Python 3. And
then, for example::
b = bytes(b'ABCD')
assert list(b) == [65, 66, 67, 68]
assert repr(b) == "b'ABCD'"
assert [65, 66] in b
# These raise TypeErrors:
# b + u'EFGH'
# b.split(u'B')
# bytes(b',').join([u'Fred', u'Bill'])
s = str(u'ABCD')
# These raise TypeErrors:
# s.join([b'Fred', b'Bill'])
# s.startswith(b'A')
# b'B' in s
# s.find(b'A')
# s.replace(u'A', b'a')
# This raises an AttributeError:
# s.decode('utf-8')
assert repr(s) == 'ABCD' # consistent repr with Py3 (no u prefix)
for i in range(10**11)[:10]:
pass
and::
class VerboseList(list):
def append(self, item):
print('Adding an item')
super().append(item) # new simpler super() function
For more information:
---------------------
- future.types.newbytes
- future.types.newdict
- future.types.newint
- future.types.newobject
- future.types.newrange
- future.types.newstr
Notes
=====
range()
-------
``range`` is a custom class that backports the slicing behaviour from
Python 3 (based on the ``xrange`` module by Dan Crosta). See the
``newrange`` module docstring for more details.
super()
-------
``super()`` is based on Ryan Kelly's ``magicsuper`` module. See the
``newsuper`` module docstring for more details.
round()
-------
Python 3 modifies the behaviour of ``round()`` to use "Banker's Rounding".
See http://stackoverflow.com/a/10825998. See the ``newround`` module
docstring for more details.
"""
from __future__ import absolute_import, division, print_function
import functools
from numbers import Integral
from future import utils
# Some utility functions to enforce strict type-separation of unicode str and
# bytes:
def disallow_types(argnums, disallowed_types):
"""
A decorator that raises a TypeError if any of the given numbered
arguments is of the corresponding given type (e.g. bytes or unicode
string).
For example:
@disallow_types([0, 1], [unicode, bytes])
def f(a, b):
pass
raises a TypeError when f is called if a unicode object is passed as
`a` or a bytes object is passed as `b`.
This also skips over keyword arguments, so
@disallow_types([0, 1], [unicode, bytes])
def g(a, b=None):
pass
doesn't raise an exception if g is called with only one argument a,
e.g.:
g(b'Byte string')
Example use:
>>> class newbytes(object):
... @disallow_types([1], [unicode])
... def __add__(self, other):
... pass
>>> newbytes('1234') + u'1234' #doctest: +IGNORE_EXCEPTION_DETAIL
Traceback (most recent call last):
...
TypeError: can't concat 'bytes' to (unicode) str
"""
def decorator(function):
@functools.wraps(function)
def wrapper(*args, **kwargs):
# These imports are just for this decorator, and are defined here
# to prevent circular imports:
from .newbytes import newbytes
from .newint import newint
from .newstr import newstr
errmsg = "argument can't be {0}"
for (argnum, mytype) in zip(argnums, disallowed_types):
# Handle the case where the type is passed as a string like 'newbytes'.
if isinstance(mytype, str) or isinstance(mytype, bytes):
mytype = locals()[mytype]
# Only restrict kw args only if they are passed:
if len(args) <= argnum:
break
# Here we use type() rather than isinstance() because
# __instancecheck__ is being overridden. E.g.
# isinstance(b'abc', newbytes) is True on Py2.
if type(args[argnum]) == mytype:
raise TypeError(errmsg.format(mytype))
return function(*args, **kwargs)
return wrapper
return decorator
def no(mytype, argnums=(1,)):
"""
A shortcut for the disallow_types decorator that disallows only one type
(in any position in argnums).
Example use:
>>> class newstr(object):
... @no('bytes')
... def __add__(self, other):
... pass
>>> newstr(u'1234') + b'1234' #doctest: +IGNORE_EXCEPTION_DETAIL
Traceback (most recent call last):
...
TypeError: argument can't be bytes
The object can also be passed directly, but passing the string helps
to prevent circular import problems.
"""
if isinstance(argnums, Integral):
argnums = (argnums,)
disallowed_types = [mytype] * len(argnums)
return disallow_types(argnums, disallowed_types)
def issubset(list1, list2):
"""
Examples:
>>> issubset([], [65, 66, 67])
True
>>> issubset([65], [65, 66, 67])
True
>>> issubset([65, 66], [65, 66, 67])
True
>>> issubset([65, 67], [65, 66, 67])
False
"""
n = len(list1)
for startpos in range(len(list2) - n + 1):
if list2[startpos:startpos+n] == list1:
return True
return False
if utils.PY3:
import builtins
bytes = builtins.bytes
dict = builtins.dict
int = builtins.int
list = builtins.list
object = builtins.object
range = builtins.range
str = builtins.str
# The identity mapping
newtypes = {bytes: bytes,
dict: dict,
int: int,
list: list,
object: object,
range: range,
str: str}
__all__ = ['newtypes']
else:
from .newbytes import newbytes
from .newdict import newdict
from .newint import newint
from .newlist import newlist
from .newrange import newrange
from .newobject import newobject
from .newstr import newstr
newtypes = {bytes: newbytes,
dict: newdict,
int: newint,
long: newint,
list: newlist,
object: newobject,
range: newrange,
str: newbytes,
unicode: newstr}
__all__ = ['newbytes', 'newdict', 'newint', 'newlist', 'newrange', 'newstr', 'newtypes']